Activated carbon adsorption is known as an efficient treatment process for water contaminated with pesticides. The adsorbability of pesticides onto activated carbon after their degradation was investigated. The degradation ratio and adsorption equilibrium were examined in batch experiments on fenitrothion and diazinon as pesticides. These concentrations and also adsorbability fell down after degradation processes including ultraviolet radiation, ozonation, hydrolysis and aerobic biodegradation. The extent of change in activated carbon adsorbability varied with the degradation processes. Degradation was found to have critical effects on adsorbability and to be important to achieve good efficiency in the water treatment system.

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In order to evaluate toxicities of pollutants to seawater fish, we examined suitable fishes for acute toxicity test. Larvae and juveniles of seven seawater fish species which are easy to rear or collect, were exposed to cadmium (Cd) and fenitrothion (MEP) for 96 hours.
While we could not calculated 72 and 96h LC₅₀ of larvae because of their mortality of control over 10% after 48 hours, all early juveniles showed incipient LC₅₀s or 96h LC₅₀s. Based on the incipient LC₅₀ or 96h LC₅₀, the order of the LC₅₀ of each fish to the pollutants were the following.
1) Cd: C. dolichognathus >G. punctata >A. schlegeli >M. cephalus >E. japonica >P. major
2) MEP : C. dolichognathus >M. cephalus, P. olivaceus >G. punctata >P. major >A. schlegeli
The red sea bream (P. major) showed the lower incipient LC₅₀s of Cd and MEP in 163mg and 510mg body weights, respectively. Based on the sensitivity to the pollutants by incipient LC₅₀ or 96h LC₅₀ and its availability, the early juvenile of red sea bream is considered the best among the fishes examined for acute toxicity test.

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The mutagenic extract of chlorinated tap water was subjected to HPLC fractionation. About 19,000l of chlorinated tap water was concentrated by XAD-4 absorption in pH 2, followed by the elution by dichloromethane. This concentrate was divided into acidic and neutral fractions. Each fraction was subjected to ODS-reversed phase HPLC fractionation. HPLC subfractions of each fraction were assayed for mutagenicity and analyzed for the strong mutagen, 3-chloro-4-dichloromethy-5-hydroxy-2(5H)-furanone (MX). Only two of nine HPLC subfractions from the acidic fraction showed significant mutagenicity, and one subfraction contained MX, which explained 55% mutagenicity of that subtraction. Another mutagenic subfraction did not contain MX. Unknown mutagens in these subfractions were presumed to have similarities to MX in their structures or chemical natures.
HPLC fractionation of neutral fraction resulted in many mutagenic subfractions. This implies that the neutral fraction contained many mutagens, which might not be similar to MX. Mutagens in this fraction have more unknown nature than the acidic fraction.
Reactivity of the mutagens and sulfite was also studied. About 60% of the mutagenicity of the tap water was destroyed after 6.5h reaction with sulfite in 1.5 chlorine equivalent concentration. 28h reaction with sulfite in 5.0 chorine equivalent concentration destroyed 76% mutagens.

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Biodegradation of tetrachloroethylene (PCE) to trichloroethylene (TCE) and cis-1,2-dichloroethylene (cis-DCE) under the anaerobic condition was studied using static soil microcosms. It was proved that the biodegradation was well approximated by a consecutive firstorder reaction model. This implied that the total of the molar concentration of the above three compounds was always constant and equaled to the initial molarity of PCE, even if the amount of each compound changed as a function of time. On the basis of these facts, two indices for the characterization of the contamination were derived : total contamination level determined as the sum of the molarities of the three compounds and degradation level defined by the total molar percentage of the products (TCE+DCE). These indices enable us to evaluate the initial concentration of the pollutant PCE and the degree of degradation.

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A simple model, which includes accmulation of inert organic solids such as decayed biomass and extracellular polymers, has been developed to predict the treatment efficiency, and to evaluate the accumulation of “active biomass” and the biofilm development in a methanogenic fluidized bed. Mass balance equations of substrate and biomass comprised additional rate terms of extracellular polymer production and biomass detachment, respectively.
The results of a steady-state analysis indicated that the biofilm contained a significant amount of inert organic solid when a lower detachment rate was given to the inert solids than the “active biomass”. The accumulation of inert organic solids might explain why reported maximum specific rates of acetate consumption for methanogenic biofilms were much lower than those of enriched and pure cultures of acetate utilizing methanogens. The conventional concept of solid retention time (SRT) seems to overestimate the true SRT of “active biomass”, which is a more useful index for controlling the treatment in fluidized beds. The model experiments also implied that maximum specific activities of total biofilm and washed-out biomass were fundamentally related to the biomass detachment rates at the biofilm surface. Determination of the activities of sloughed biomass would be useful to investigate the bacterial distribution in biofilms.

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Accumulation of inert organic solids within biofilm in a methanogenic fluidized bed was investigated by conducting a continuous feed experiment in which the influent substrate concentration was stepwise increased. The previously developed model considering accumulation of inert organic solids and biomass detachment was applied to the simulations of biofilm growth and treatment efficiency in the above-mentioned experiment.
The transient response of treatment were well explained with the model by giving the growth kinetic constants and the detachment coefficients of the responsible “active biomass”, whose concentrations were defined with the substrate consumption activities. The biofilm growth was deeply associated with the accumulation of inert organic solids, the rate of which depended on the decay coefficient and the growth yields of “active biomass” as well as the detachment coefficient. The detachment coefficient was estimated to be much smaller for decayed biomass than “active biomass” and bio-polymer. The attached biomass in the methanogenic fluidized bed contained a significant amount of bio-polymers which reached around 8 to 10% of total organic solids of biofilm. The production rate coefficient was estimated at 0.4 to 0.5 [mgCOD_Poly·mgCOD_cell^-1] with the assumed growth yield of 0.05 [mgCOD_cell·mgCOD^-1].

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Removal of nitrate ion by means of endogeneous denitrification is suitable for treatment of nitrate-polluted ground water utilized as drinking water, since in the case of endogeneous denitrification, introduction of organics as proton donor is not needed.
In this case bacteria utilizes organic substances accumulated in the bacteria itself as proton donor. Thus accumulation and utilization of organics in the bacterial biomass become important processes for effective use of this function.
Uptake and accumulation of organics are measured experimentally and the conditions necessary for accumulation was determined as well as maximum accumulation capacity and uptake rate.
Also endogenous denitrification rate and capacity by using accumulated organics was determined. On the basis of these parameters, mathematical models for describing accumulation step and denitrification step are proposed and calculation was carried out for cyclic process involving repeated accumulation and denitrification steps. The reasonable agreement between measured concentrations and calculated ones suggests the possibility of application of this process to the treatment of ground water.

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